Surface treatment apparatus and surface treatment method

ABSTRACT

HF-originated radicals generated in a plasma-forming chamber are fed to a treatment chamber via feed holes, while HF gas molecules as the treatment gas are supplied to the treatment chamber from near the radical feed holes to suppress the excitation energy, thereby increasing the selectivity to Si to remove a native oxide film. Even with the dry-treatment, the surface treatment provides good surface flatness equivalent to that obtained by the wet-cleaning which requires high-temperature treatment, and further attains growth of Si single crystal film on the substrate after the surface treatment. The surface of formed Si single crystal film has small quantity of impurities of oxygen, carbon, and the like. After sputtering Hf and the like onto the surface of the grown Si single crystal film, oxidation and nitrification are applied thereto to form a dielectric insulation film such as HfO thereon, thus forming a metal electrode film. All through the above steps, the substrate is not exposed to atmospheric air, thereby suppressing the adsorption of impurities onto the interface, and thus obtaining a C-V curve with small hysteresis. As a result, good device characteristics are obtained in MOS-FET.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication No. PCT/JP2007/071393, filed on Nov. 2, 2007, the entirecontents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method ofmanufacturing a semiconductor device, including the treatment of surfaceof group IV semiconductor.

2. Related Background Art

Conventionally semiconductor Si substrate is subjected to wet-cleaning.The wet-cleaning has, however, problems of failing to completely removewater-marks in dry state, failing to control etching of very thin oxidefilm, requiring large apparatus, and the like. Furthermore, when thesemiconductor substrate is exposed to atmospheric air for a long timeafter the wet-cleaning, there arise problems of forming native oxidefilm on the surface thereof and adsorbing carbon atoms thereon toinhibit film-forming of Si single crystal, generating irregular profileof film, generating impurity level at the interface of gate insulationfilm, and the like.

Therefore, surface oxide film was removed by applying UHV vacuum heatingto 750° C. or higher or by applying heating to 800° C. or higher in anH₂ atmosphere before film formation. However, as miniaturization ofdevice progresses and dielectric insulation film/metal electrode isused, the device needs to be manufactured at lower temperatures. Thusthe device manufacturing needs to be done at 650° C. or lowertemperature. As a result, the wet-cleaning has its limits, and therearises a need of dry-cleaning method which conducts treatment ofsemiconductor substrate in a vacuum before film-forming. The reversesputtering method using argon plasma is one example of the method(Japanese Patent Laid-Open No. 10-147877). The disclosed method,however, presumably cuts also the Si—Si bond on the surface of thesemiconductor substrate. In that case, problems arise such that oxidefilm is immediately formed on the Si-absent portion, that contaminantslikely adhere to the dangling bond of Si, and that the sputtered oxideand contaminants adhere again to the side wall of the substrate. Theseproblems adversely affect the succeeding step, (such as inhibition ofepitaxial growth and formation of highly resistant portion on thesilicide interface). Furthermore, damages on the device are also theproblem.

Japanese Patent Laid-Open No. 2004-63521 describes that, after removingthe silicon oxide film from the surface of the substrate using aplasmatized F₂ gas, the hydrogen radicals are irradiated to remove the Fcomponent adhered to the surface of the substrate. Japanese PatentLaid-Open No. 04-96226 describes that, after removing the Si nativeoxide film from the surface of the substrate using F₂ gas, theradicalized hydrogen is irradiated to the substrate to terminate thebonding operation by the hydrogen. Since, however, the plasmatized F₂gas contains not only the radicalized fluorine gas but also ionizedfluorine gas, there arises a problem of irregular surface on removingthe silicon oxide film from the surface of the substrate. In addition,there may occur also the removal of a portion of substrate not only theremoval of silicon oxide film on the surface thereof.

Japanese Patent Laid-Open No. 2001-102311 describes that a cleaning gassuch as fluorine is supplied to a plasma-forming part having aplasma-forming chamber which is separated by a plate having feed holesfor a film-forming chamber where the substrate is placed, thusgenerating radicals by generating plasma in the plasma-forming part, andthe fluorine radicals are fed to a film-forming space containing thesubstrate via the feed holes, thereby irradiating the radicals to thesubstrate to clean the substrate. Since, however, the surface of thesemiconductor substrate cannot be exposed to the atmosphere where theexcitation energy of radicals is suppressed, highly selective Si etchingcannot be performed, which raises a problem of failing to remove thenative oxide film without deteriorating the surface roughness.

Furthermore, since the semiconductor substrate is exposed to plasma,Si—Si bond is also cut off. In this state, there arise problems suchthat oxide film is immediately formed on the Si-absent portion, thatcontaminants likely adhere to the dangling bond of Si, and that thesputtered oxide and contaminants adhere again to the side wall of thesubstrate. These problems adversely affect the succeeding stage, (suchas inhibition of epitaxial growth and formation of highly resistantportion on the silicide interface). Furthermore, damages on a device arealso the problem. According to the disclosure, gas is decomposedpositively by plasma to generate hydrogen radicals and hydrogen ions.When fluorine residue on the surface of the substrate is removed by thehydrogen radicals and the hydrogen ions, there arise problems ofcontamination by metal coming from the chamber, of excess etchingbecause of large etching rate on the base Si, and the like. Furthermore,since HF as the reaction product likely adheres again to the surface ofthe substrate, sufficient F-removal effect is not attained. JapanesePatent Laid-Open No. 2002-217169 discloses an apparatus for conductingentire cleaning step in a vacuum to remove foreign matter applyingsimultaneously a physical action of friction stress generated by a highvelocity gas flow. According to the disclosure, adsorption of impuritiesand generation of native oxide during vacuum transfer are suppressed,thus improving the production efficiency. Even if the foreign matter canbe removed, however, the native oxide film and the surface roughnessremain on the surface at an order of atomic layer thickness. That is, toattain the effect of device characteristic improvement by the continuoustransfer in vacuum, there are required the cleaning technology tocontrol the highly selective etching of Si and native oxide film at anorder of atomic layer thickness, and the transfer of substrate and thefilm-forming thereon without exposing the substrate to atmospheric air.That kind of control technology and vacuum operation should provide gooddevice characteristics of low interface state at the joint betweensemiconductor and dielectric insulation film, and of small fixed chargein the film.

SUMMARY OF INVENTION Problems to be Solved by the Invention

According to the surface treatment in the related art to remove nativeoxide film and organic matter from the substrate surface, the transferin atmospheric air is required before the substrate arrives at the nextfilm-forming step. During the transfer of the substrate in atmosphericair, substances in air adsorb onto the surface of the substrate, andnative oxide film and impurities such as carbon atoms are left behind onthe interface, which raises a problem of deterioration of devicecharacteristics. When the substrate treatment is conducted in a vacuumnot to leave the native oxide film and the impurities such as carbonatoms on the interface, the flatness of the substrate surface isdeteriorated, though the native oxide film and the impurities such asorganic matter and carbon on the substrate surface can be removed.Furthermore, poor flatness of the substrate surface raises a problem ofdeteriorating the characteristics of manufactured device.

Means to Solve the Problems

The present invention is made to solve the above problems. According tothe investigations of the inventors of the present invention, radicalsgenerated by plasma are fed to the treatment chamber via a plurality ofholes formed on a partition plate which separates the plasma-formingchamber from the treatment chamber, the radicals are mixed with atreatment gas which is separately fed to the treatment chamber, thussuppressing the excitation energy of the radicals to thereby enable thesubstrate surface treatment at high Si-selectivity, and thus it is foundout that the surface treatment becomes available which removes nativeoxide film and organic matter without deteriorating the flatness of thesubstrate surface.

The present invention provides a method of cleaning a substratecomprising the steps of: placing a substrate in a treatment chamber;turning a plasma-forming gas; feeding a radical in the plasma to thetreatment chamber via a radical-passing hole of a plasma-confinementelectrode plate for plasma separation; feeding a treatment gas to thetreatment chamber to mix it with the radical in the treatment chamber;and cleaning the surface of the substrate by the mixed atmosphere of theradical and the treatment gas.

The present invention provides a method of cleaning a substrate, whereinthe surface of the substrate is a group IV semiconductor material, andthe plasma-forming gas and the treatment gas contain HF, respectively.

The present invention provides a method of cleaning a substrate, whereinthe plasma-confinement electrode plate for plasma separation has aplurality of radical feed holes for feeding the radical in the plasma tothe treatment chamber and a plurality of treatment gas feed holes forfeeding the treatment gas into the treatment chamber, and thus theradical and the treatment gas are discharged toward the surface of thesubstrate in the treatment chamber via the respective feed holes.

The present invention provides a method of manufacturing a semiconductordevice comprising the steps of: cleaning the surface of a group IVsemiconductor substrate in a cleaning chamber in accordance with theabove method; transferring the cleaned substrate from the cleaningchamber to an epitaxial chamber via a transfer chamber without exposingthe substrate to atmospheric air; and epitaxially growing an epitaxialsingle crystal layer on the surface of the substrate in the epitaxialchamber.

The present invention provides a method of manufacturing a semiconductordevice comprising the steps of: transferring a substrate having anepitaxial layer manufactured in accordance with the above method fromthe epitaxial chamber to a sputtering chamber via a transfer chamberwithout exposing the substrate to atmospheric air; sputtering adielectric film onto the epitaxial layer in the sputtering chamber;transferring the substrate having the dielectric film thereon from thesputtering chamber to an oxidation-nitrification chamber via a transferchamber without exposing the substrate to atmospheric air; andconducting oxidation, nitrification, or oxynitrification of thedielectric film in the oxidation-nitrification chamber.

The present invention provides a method of manufacturing a semiconductordevice according to above method, wherein the dielectric film is made ofthe one selected from the group consisting of Hf, La, Ta, Al, W, Ti, Si,and Ge, or an alloy thereof.

The present invention provides a method of cleaning a substrateaccording to above method, wherein turning the plasma-forming gas intoplasma is done by applying a high frequency power thereto, and thedensity of the high frequency power is in a range from 0.001 to 0.25W/cm², preferably from 0.001 to 0.125 W/cm², and more preferably from0.001 to 0.025 W/cm².

The present invention provides a substrate treatment apparatus ofplasma-separation type generating a radical by forming plasma from aplasma-forming gas in a vacuum chamber, and conducting substratetreatment by the radical and a treatment gas, the substrate treatmentapparatus comprising: a plasma-forming chamber for turning theplasma-forming gas fed therein into plasma; a treatment chambercontaining a substrate holder on which a substrate to be treated isplaced; and a plasma-confinement electrode plate for plasma separationhaving a plurality of radical-passing holes formed between theplasma-forming chamber and the treatment chamber, the plasma-confinementelectrode plate of a hollow structure having a plurality of treatmentgas feed holes opened toward the treatment chamber formed, and having agas-feed pipe for supplying the treatment gas disposed, wherein: aplasma-forming space inside the plasma-forming chamber contains ahigh-frequency applying electrode for generating plasma by a powersupplied from a high-frequency power source; the high-frequency applyingelectrode has a plurality of through-holes penetrating therethrough; thehigh-frequency applying electrode further contains a plasma-forming gasfeed shower plate for feeding the plasma-forming gas to theplasma-forming chamber; and the plasma-forming gas feed shower plate hasa plurality of gas-discharge ports for feeding the plasma-forming gasonto the electrode extending along the plasma-confinement electrodeplate for plasma separation provided with the plurality ofradical-passing holes.

The present invention provides a substrate treatment apparatus accordingto above apparatus, wherein, in the substrate treatment chamber, thevolume ratio V2/V1 is in a range from 0.01 to 0.8, where V2 is the totalvolume of the plurality of through-holes of the electrode, and V1 is thetotal volume of the electrode including the through-holes.

The present invention provides a substrate treatment apparatus accordingto above apparatus, wherein the density of the high frequency powerapplied to the high frequency-applying electrode is in a range from0.001 to 0.25 W/cm², preferably from 0.001 to 0.125 W/cm², and morepreferably from 0.001 to 0.025 W/cm².

The present invention provides a substrate treatment apparatus accordingto above substrate, wherein the plasma-forming gas fed to theplasma-forming chamber is a gas containing HF, and the gas fed to thetreatment chamber is a gas containing HF.

The present invention provides an apparatus of manufacturingsemiconductor device comprising: a substrate cleaning chamber includingthe above substrate treatment apparatus; an epitaxial growth chamberforming an epitaxial layer on the substrate; and a transfer chambertransferring the substrate coming from the substrate cleaning chamber tothe epitaxial growth chamber without exposing the substrate toatmospheric air.

The present invention provides an apparatus of manufacturing asemiconductor device according to above apparatus, further comprising asputtering chamber forming a dielectric film, thus allowing transferringthe substrate coming from the cleaning chamber or the epitaxial growthchamber to the sputtering chamber via the transfer chamber withoutexposing the substrate to atmospheric air.

The present invention provides an apparatus of manufacturing asemiconductor device according to above apparatus, further comprising anoxidation-nitrification chamber for oxidation, nitrification, oroxynitrification of the dielectric film, thus allowing transferring thesubstrate coming from the cleaning chamber, the epitaxial growthchamber, or the sputtering chamber to the oxidation-nitrificationchamber via the transfer chamber without exposing the substrate toatmospheric air.

EFFECT OF THE INVENTION

The present invention performs substrate treatment which can decreasethe native oxide film and organic impurities on the surface ofsemiconductor substrate compared with the wet-cleaning in the relatedart, and can remove the native oxide film and organic matter withoutdeteriorating the flatness of the substrate surface.

According to the present invention, to remove the native oxide film andcontamination of organic impurities from the surface of semiconductorsubstrate, HF gas or a mixed gas containing at least HF is used as theplasma-forming gas and the treatment gas, and radicals are fed from theplasma-forming chamber to the treatment chamber, while feedingsimultaneously gas molecules containing HF as the structural elementthereto, thus exposing the surface of semiconductor substrate to theabove atmosphere which suppresses the excitation energy of the radicals,to thereby remove the native oxide film and organic matter withoutdeteriorating the flatness of the substrate surface. There generates nometal contamination and plasma damage on the semiconductor substrate.Although the wet-cleaning in the related art needs more than one stepfor the substrate treatment applying also succeeding steps such asannealing treatment, the present invention performs the substratetreatment in only one step, which attains desired effect efficiently,reduces cost, and significantly improves the treatment speed.Furthermore, use of a shower plate to the plasma-forming gas allowsuniform feeding of the product gas, use of through-holes on theelectrode part allows discharge even at a low power, and use of aplasma-confinement electrode plate for plasma separation provided with aplurality of radical-passing holes allows radicals in the producedplasma to be fed uniformly to the treatment chamber. Actualizing thesurface treatment to give fine surface roughness at an order of atomiclayer thickness allows forming single crystal Si and SiGe films on thesurface.

By the first step of conducting substrate surface treatment, and thesecond step of transferring the substrate without exposing the singlecrystal film to atmospheric air, the amount of impurities at theinterface is smaller than that appears in the atmospheric transfer, andthus good device characteristics are attained.

By conducting the first step of conducting substrate surface treatment,the second step of forming single crystal film, the third step ofsputtering the dielectric material to form a film, the fourth step ofconducting oxidation, nitrification, or oxynitrification, and the fifthstep of transferring the metallic material and the sputtered film in avacuum without exposing thereof to atmospheric air, the amount ofimpurities on the joint interface between the semiconductor and theinsulation film becomes smaller than that in atmospheric transfer, whichprovides the interface state density and the fixed charge density infilm equivalent to those of oxide film attained in the related art,gives a C-V curve with small hysteresis, gives a small leak current, andthereby attains good device characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a configuration example of afilm-forming apparatus used in the present invention.

FIG. 2 is a schematic diagram of a controller installed in the apparatusused in the present invention.

FIG. 3 is a schematic diagram of a configuration example of a surfacetreatment apparatus used in the present invention.

FIG. 4 is a schematic diagram of a configuration example of ahigh-frequency applying electrode part of the surface treatmentapparatus used in the present invention.

FIG. 5 is a schematic diagram of a configuration example of aplasma-confinement electrode plate part of the surface treatmentapparatus used in the present invention.

FIG. 6 is a graph showing a native oxide film/Si with variedhigh-frequency power density, obtained in an example of the presentinvention.

FIG. 7 is a schematic diagram of a configuration example of a UV, X-rayand microwave excited radical surface treatment apparatus used in thepresent invention.

FIG. 8 is a schematic diagram of a configuration example of acatalytic-chemical excited radical surface treatment apparatus used inthe present invention.

FIG. 9 is a schematic diagram of a surface treatment method used in thepresent invention.

FIG. 10 is a flowchart of a transfer controller program used in thepresent invention.

FIG. 11 is a flowchart of a film-forming controller program used in thepresent invention.

FIG. 12 gives a graph showing the surface roughness (Ra) after treatmentof the substrate, and SEM images on the surface, obtained by an exampleof the present invention.

FIG. 13 is a graph showing the surface roughness (Ra) relative to thefraction of treatment chamber gas with varied fraction of theplasma-forming gas, obtained by an example of the present invention.

FIG. 14 gives SEM images on the surface after the growth of Si and SiGe,obtained by an example of the present invention.

FIG. 15 is a graph showing the atom density of oxygen and carbon at aninterface, obtained by an example of the present invention.

FIG. 16 is a C-V curve obtained by an example of the present invention.

FIG. 17 shows a comparison of the interface state density and the fixedcharge density, between those obtained by an example of the presentinvention and those of oxide film in the related art.

FIG. 18 is a graph showing the relation between the equivalent oxidefilm thickness (EOT) and the leak current, obtained by an example of thepresent invention.

FIG. 19 is a diagram illustrating a MOS-FET manufactured by thetreatment of the present invention.

FIG. 20 is a diagram of the substrate intraplane distribution of theetching rate of the silicon oxide film, showing the effect of thegas-feeding shower plate for the plasma-forming gas to the plasmachamber of the present invention.

EXAMPLES

The examples of the present invention will be described below.

The embodiments of the present invention will be described belowreferring to the drawings.

The examples deal with the cases of applying the present invention to afilm-forming apparatus 1 illustrated in FIG. 1, focusing on the processof removing native oxide film and organic matter formed on a Sisubstrate by the first step using a surface treatment apparatus 100illustrated in FIG. 3.

A substrate 5 which is adopted as the sample is a Si single crystalsubstrate (with 300 mm in diameter) which is allowed to stand in a cleanair to form a native oxide film thereon. The substrate 5 is transferredto a load-lock chamber 50 by a substrate transfer mechanism (not shown)to be placed therein. Then, the load-lock chamber 50 is evacuated by anevacuation system (not shown). After evacuating to a desired pressure,or 1 Pa or below, a gate valve (not shown) between the load-lock chamberand the transfer chamber is opened, and a transfer mechanism (not shown)in the transfer chamber transfers the substrate 5 to the surfacetreatment apparatus 100 via the transfer chamber 60, and places thesubstrate 5 on a substrate holder 114.

FIG. 3 illustrates the surface treatment apparatus 100 of the presentinvention.

The surface treatment apparatus 100 is composed of a treatment chamber113 equipped with the substrate holder 114 on which the substrate 5 canbe placed, and a plasma-forming chamber 108. The treatment chamber 113and the plasma-forming chamber 108 are separated from each other by aplasma-confinement electrode plate 110 for plasma separation providedwith a plurality of radical-passing holes 111.

The plasma-forming gas is fed from a plasma-forming gas supply system101 to pass through a plasma-forming gas supply pipe 102, and enters aplasma-forming space 109 in the plasma-forming chamber 108 viaplasma-forming gas feed holes 106 opened on a plasma-forming gas feedshower plate 107. With this arrangement, the plasma-forming gas canenter uniformly the plasma-forming space 109 in the plasma-formingchamber 108.

FIG. 20 illustrates the effect of plasma-forming gas feed shower plate107 in the examples. The etching rate of the silicon oxide film on thesubstrate placed in the treatment chamber was determined using HF gas asthe plasma-forming gas at a flow rate of 100 sccm, 0.01 W/cm² ofhigh-frequency power density, and 50 Pa of treatment chamber pressure.In FIG. 20, the horizontal axis is a wafer position in the substrateplane, and the vertical axis is the etching rate of the silicon oxidefilm normalized by the etching rate at the center position. As shown inFIG. 20, when the case 901 which applied the plasma-forming gas feedshower plate is compared with the case 902 which did not apply theplasma-forming gas feed shower plate and applied lateral directionalfeed, as the feed method of the related art, the case 901 of feedingthrough the shower plate gave better uniformity in the in-plane etchingrate. Presumable cause of the result is that the uniform gas feed to theplasma-forming space 109 secured uniform concentration distribution ofactive species in the plasma-forming space 109, and the phenomenoncontributed to the result. Consequently, together with the effect ofuniform plasma-forming owing to through-holes 105 of a high-frequencyapplying electrode 104 described below, there was confirmed furtheruniform radical supply to the treatment chamber.

The high-frequency applying electrode 104 extends along theplasma-forming gas feed shower plate 107 at above thereof or along theplasma-confinement electrode plate 110 for plasma separation at belowthereof so as to divide the plasma-forming chamber 108 into twosegments, upper one and lower one. The high-frequency applying electrode104 is provided with through-holes 105. By applying high frequency powerfrom a high frequency power source 103 to the high-frequency applyingelectrode 104, plasma is generated.

The plasma-confinement electrode plate 110 for plasma separation has afunction of plasma-confinement electrode plate for plasma separation topartition the plasma-forming chamber 108 from the treatment chamber 113.The plasma-confinement electrode plate 110 is provided with theradical-feed holes 111 which allow radicals to pass therethrough to thetreatment chamber 113, while rejecting the ions in the plasma in theplasma chamber.

The plasma-confinement electrode plate 110 for plasma separation has ahollow structure, and is provided with a plurality of treatment gas feedholes opened toward the treatment chamber. By supplying the treatmentgas to the hollow structure, the treatment gas can be uniformly suppliedto the treatment chamber via the plurality of treatment gas feed holes112 opened toward the treatment chamber. The treatment gas feed holes112 open in the vicinity of the respective radical feed holes 111. Thetreatment gas passes through a treatment gas supply pipe 115 from atreatment gas supply system 116, and enters the treatment chamber viathe plurality of treatment gas feed holes 112 opened toward thetreatment chamber. The radicals, originated from the plasma-forming gas,fed from the radical feed holes 111 and the molecules of treatment gasfed from the treatment gas feed holes 112 are mixed together in thetreatment chamber 113 for the first time, and the mixture is thensupplied to the surface of the substrate 5.

As described above, the radicals originated from the plasma-forming gasare fed to the treatment chamber 113 via the radical feed holes 111formed on the plasma-confinement electrode plate 110 which partitionsthe treatment chamber 113 from the plasma-forming chamber 108. Only themolecules and atoms which are electrically neutral, such as radicals,are allowed to pass through the radical feed holes 111 opened on theplasma-confinement electrode plate 110 from the plasma-forming chamber108 to enter the treatment chamber 113, and very few ions in plasma areallowed to enter the treatment chamber 113. In the plasma-formingchamber 108, when the ion density is about 1×10¹⁰ count/cm³, the iondensity in the treatment chamber becomes about 5×10² count/cm³, thus theion density is decreased to less than one to ten million, which can besaid that substantially very few ions enter the treatment chamber. Incontrast, regarding the radicals, about several percentages to severaltens of percentages of the generated ones, depending on the life, in theplasma-forming chamber are transferred to the treatment chamber.

The through-holes 105 in the high-frequency applying electrode 104adopted the shape illustrated in FIG. 4. Since the electrodethrough-holes 105 allow the electrode to further uniformly dischargeeven at a low power of 0.25 W/cm² or less, the radicals are feduniformly to the treatment chamber. The volume ratio of the total volumeof a plurality of through-holes of the electrode V2 to the total volumeof the high-frequency applying electrode including the through-holes V1,V2/V1, is preferably in a range from 0.01 to 0.8. When V2/V1<0.01, thedeterioration of radical distribution appeared. When V2/V1>0.8,discharge failed.

The method of manufacturing a semiconductor device using thefilm-forming apparatus 1 illustrated in FIG. 1 of the present inventionwill be described below.

The description begins with the substrate treatment step as the firststep, and with the condition of the step. The apparatus used in thefirst step is the substrate treatment apparatus 100 illustrated in FIG.3.

As the plasma-forming gas, HF at 100 sccm of the flow rate was suppliedto the plasma-forming chamber 108, thus generated plasma in theplasma-forming part. The radicals in the generated plasma were suppliedto the treatment chamber 113 via the radical feed holes (radical passingholes) 111 formed in the plasma-confinement electrode plate 110 forplasma separation. To suppress the excitation energy of the radicals, HFas the treatment gas was supplied to the treatment chamber 113 via thetreatment gas feed holes 112 at a flow rate of 100 sccm. The highfrequency power density for plasma generation was 0.01 W.cm², thepressure was 50 Pa, the treatment time was 5 min, and the temperature ofthe substrate 5 was 25° C.

FIG. 12 shows the observed surface roughness after the first step of thepresent invention, with the comparison with the result of conventionaldry-treatment and wet-treatment. As shown in FIG. 12, the surfaceroughness Ra obtained from the first step of the present invention was0.18 nm, which is a good level almost equal to the surface roughness Raof 0.17 nm obtained by the wet treatment (wet-cleaning) with a dilutehydrofluoric acid solution. For the case of not supplying the HF gas asthe treatment gas, the surface roughness Ra became 2.0 nm, which is arough level. Furthermore, even when the treatment time was extended to10 min, the surface roughness Ra was confirmed to 0.19 nm, which is nota rough level. The improved surface flatness owes the selective removalof the surface native oxide film and organic matter in relation to Si.Presumable mechanism is that the high excitation energy HF generatedfrom plasma is brought to collide with the unexcited HF separately fedas the treatment gas, thus forming HF having suppressed excitationenergy, and the suppressed excitation energy HF selectively removes thesurface native oxide film while not etching the Si atoms on the surface.The observed results confirmed that the use of the present invention canrealize the surface flatness, equivalent to that of the wet-cleaning, bythe dry-cleaning which does not need the high temperature pretreatment.

The condition to attain the surface flatness according to the presentinvention is only to form HF having suppressed excitation energy bymixing and colliding an HF having high excitation energy generated fromthe plasma with an HF of unexcited separately fed as the treatment gas.Consequently, the structure of the example is not limited if only theabove condition is satisfied.

That is, according to this example, the radicals generated by the plasmaare supplied to the substrate via the radical feed holes as theplurality of through-holes in the plasma-confinement electrode plate,while supplying the treatment gas via the plurality of treatment gassupply holes formed in the electrode plate. To obtain the flatness,however, the structure is not necessarily limited to the one given inthis example, and the effect can be obtained by plasmatizing the gascontaining HF gas, and by feeding solely the excited active species tothe treatment chamber using an apparatus which allows only the neutralactive species to pass therethrough while rejecting most of the ions,and further by feeding an unexcited HF gas from any part of thetreatment chamber.

From the point of uniformity, however, and specifically when uniformtreatment is required to a large diameter substrate, it is necessary tosupply both the radicals and the unexcited treatment gas uniformly tothe substrate. To this end, as in this example, it is preferable toadopt the structure which allows radicals to be shower-supplied from theelectrode plate facing the substrate, and allows also the treatment gasto be shower-supplied at the same time.

Although the example conducts the radical generation by the plasmaformation by the high frequency application, the radical generation maybe done by the plasma formation by microwave and other methods. Indetail, there can also be applied the radical generation through UV,X-ray, and microwave excitation given in FIG. 7, and thecatalyst-chemical excitation given in FIG. 8. In FIG. 7, UV, X-ray, andmicrowaves are irradiated to the plasma gas from a feed chamber 203 toturn the plasma gas into plasma. In FIG. 7, reference numeral 5signifies the substrate; 201, the plasma-forming gas supply system; 202,the plasma-forming gas supply pipe; 204, the plasma-confinementelectrode plate for plasma separation provided with a plurality ofradical-passing holes; 205, the radical feed hole; 207, the treatmentchamber; 208, the substrate holder; 209, the treatment gas supply pipe;210, the treatment gas supply system; and 211, the exhaust system. Thetreatment gas system has the same configuration as that of FIG. 3. FIG.8 illustrates the configuration of turning the gas into plasma by aheating catalyst body 303. Reference numeral 5 signifies the substrate;301, the plasma-forming gas supply system; 302, the plasma-forming gassupply pipe; 304, the plasma-confinement electrode plate for plasmaseparation provided with a plurality of radical-passing holes; 305, theradical feed hole; 306, the treatment gas feed hole; 307, the treatmentchamber; 308, the substrate holder; 309, the treatment gas supply pipe;310, the treatment gas supply system; and 311, the exhaust system. Thetreatment gas system has the same configuration as that of FIG. 3.

Regarding the plasma-forming gas fed to the plasma-forming chamber, theexample used only HF. The plasma-forming gas is only required to containat least HF, and specifically HF diluted with Ar may be used. Bygenerating plasma, and by passing the plasma through theplasma-confinement electrode plate 110, the radicals enter the treatmentchamber 113. For the treatment gas entering the treatment chamber 113,the example used only HF. The treatment gas is only required to containat least HF, and specifically HF diluted with Ar may be used. By mixingthe radicals which were fed to the treatment chamber 113 via the radicalfeed holes 111 opened on the plasma-confinement electrode plate 110 withthe treatment gas fed from the treatment gas feed holes 112, there iscreated an atmosphere in which the excitation energy of radicals issuppressed. Then, the native oxide film and the organic matter on thesurface of the substrate are selectively removed in relation to Si ofthe substrate material, thereby performing the substrate surfacetreatment while suppressing the surface roughening.

From the point of surface roughness after the substrate treatment, thefraction of HF flow rate to the total gas flow rate is preferably in arange from 0.2 to 1.0. The experimental result confirming the fractionrange is described below.

FIG. 13 shows the dependency of the surface roughness on the HF mixingratio in the case of using a mixed gas of HF with Ar as theplasma-forming gas and the treatment gas, respectively. As shown in FIG.13, varying the mixing ratio of HF to Ar in the treatment gas varied thesurface roughness after removing the native oxide film. Increase in theHF gas flow rate decreased the surface roughness. Even when the HF gaswas used as the plasma-forming gas to be supplied to the plasma-formingchamber 108, and when the radicals were supplied via the radical feedholes 111 formed in the plasma-confinement electrode plate 110 forplasma separation, the case of supplying sole Ar as the treatment gasfailed to remove the native oxide film on the substrate surface, andfailed to attain the purpose of desired surface treatment. As for thecase of supplying HF gas as the plasma-forming gas and of absence of thetreatment gas, the surface roughness Ra became 2.5 nm, worsened comparedwith the case of using HF gas. The example used a Si substrate. However,the substrate surface treatment of the present invention does not limitto the surface treatment of Si substrate. In concrete terms, the requestis only to structure the substrate surface with a group IV semiconductorsuch as Si and SiGe. More specifically, the substrate surface treatmentcan be applied to the one for removing native oxide film and organiccontamination on the surface of group IV semiconductor such as thin Silayer which is adhered to or deposited on a glass substrate.

The high frequency power density applied onto the high-frequencyapplying electrode 104 is preferably in a range from 0.001 to 0.25W/cm².

FIG. 6 shows the dependency of the native oxide film/Si, (etching rateratio of native oxide film to Si), on the high frequency power densityfor the case of using HF gas as the plasma-forming gas and using HF asthe treatment gas. Decrease in the high frequency power densitysuppresses the Si etching, and thus only the native oxide film isselectively etched. The value of the amount of etching the native oxidefilm divided by the amount of etching the Si is defined as “native oxidefilm/Si”. Decrease in the high frequency power density relativelydecreases the amount of etching of Si so that the “native oxide film/Si”increases. On the other hand, increase in the high frequency powerdensity significantly increases the etching of Si, thus decreasing the“native oxide film/Si”. Increase in the high frequency power densityinduces the etching of Si, which roughens the surface. To decrease thesurface roughening, it is necessary to increase the “native oxidefilm/Si” and to decrease the high frequency power density. To this end,the high frequency power density is selected to above range of from0.001 to 0.25 W/cm², preferably from 0.001 to 0.125 W/cm², and morepreferably from 0.001 to 0.025 W/cm².

Then, the description is given to the Si and SiGe epitaxial singlecrystal growth step as the second step, and to the condition thereof.

The description is for the process in which the first step is conductedusing the film-forming apparatus 1 given in FIG. 1 and using the surfacetreatment apparatus 100 given in FIG. 3 to remove the native oxide filmformed on the Si substrate, then the substrate is transferred to a CVDapparatus 20 via the vacuum transfer chamber 60 to be subjected to thesecond step, which grows the Si and SiGe single crystal film on thetreated surface of the substrate.

The substrate was treated on the surface thereof in the first step, andthen was treated in the CVD apparatus 20 as the second step under thecondition of: substrate temperature of 600° C., Si₂H₆ supply at 36 sccm,pressure holding at 2E-3 Pa, for 3 minutes. After that, the substratewas treated therein under the condition of: substrate temperature of600° C., Si₂H₆ and GeH₄ supply at 36 sccm, respectively, pressureholding at 4E-3 Pa, for 3 minutes. Thus treated substrate gave a surfaceroughness of the SiGe single crystal growth on the Si equivalent to thesurface roughness of the substrate treated by wet cleaning using adiluted hydrofluoric acid, providing a good SiGe single crystal film, asshown in FIG. 14. As given in FIG. 15, compared with the case of wetcleaning followed by the above Si/SiGe growth, the case of this examplegave smaller atom density of oxygen and carbon at the interface betweenthe Si substrate and the grown Si. In concrete terms, the atom densityof oxygen and carbon at the interface was 2×10²⁰ atoms/cm³ or less. Thephenomenon owes to the suppress of adsorption of oxygen and carbonimpurities onto the surface by the vacuum transfer of the substratewithout exposing thereof to atmospheric air after cleaning. In theprocess of growth of Si and SiGe single crystal film in the CVDapparatus 20, there can be used: a hydrogenated gas such as Si₂H₆ andGeH₄; a mixture of a hydrogenated gas with a doping material gas such asB₂H₆, PH₃, and AsH₃; or SiH₄ instead of Si₂H₆.

The description is given to the dielectric film sputtering film-formingstep as the third step, the oxidation-nitrification step of the formeddielectric film as the fourth step, and the electrode sputtering step asthe fifth step.

Succeeding to the second step, the substrate is subjected to a processto manufacture the FET device. The process comprises: the third step ofsputtering film-formation of the dielectric material in a sputteringapparatus 40 via the transfer chamber 60; the fourth step oftransferring the substrate through the transfer chamber 60 to theoxidation-nitrification apparatus 30 to oxidize the dielectric materialtherein; and the fifth step of transferring the substrate through thetransfer chamber 60 to the sputtering apparatus 40 to sputter the metalelectrode material therein. The apparatus 10 through 50 are eachcontrolled by the respective transfer or process controllers 70 through74. The dielectric material film-forming in the third step may be doneby CVD other than sputtering. Similarly, the film-forming of metalelectrode material in the fifth step may be conducted by CVD other thansputtering.

With the surface treatment apparatus 100 illustrated in FIG. 3, thefirst step was conducted to remove the native oxide film, and the secondstep was conducted to grow the Si single crystal film. Then, thesubstrate 5 passed through the vacuum transfer chamber 60 to enter thedielectric-electrode sputtering apparatus 40 without exposing thesubstrate to atmospheric air, where the sputtering film-formation of Hfwas conducted, and the substrate was transferred to theoxidation-nitrification apparatus 30 via the vacuum transfer chamber 60to oxidize the formed dielectric material film without exposing thesurface of the dielectric material to atmospheric air, thus conductedplasma and radical oxidation. Furthermore, the substrate 5 wastransferred to the dielectric-electrode sputtering apparatus 40 via thevacuum transfer chamber 60 without exposing the substrate to atmosphericair, thus sputtered to form the film of TiN electrode. Thecharacteristics of the obtained device were evaluated. The data aregiven in FIG. 16, FIG. 17, and FIG. 18.

FIG. 16 shows a C-V curve drawn by measuring the capacitance of a sampleprepared by the present invention and by the related art (wet cleaningwas applied instead of the first step), respectively, applying voltageto the electrode part. Compared with the sample of the related art whichprovided hysteresis of about 30 mV, the sample of the present inventionattained good result of 10 mV of hysteresis.

FIG. 17 shows a comparison of the interface state density and the fixedcharge density, between those obtained by the present invention andthose obtained in the related art (wet cleaning was applied instead ofthe first step). Samples were prepared by the process of the presentinvention to determine the C-V curve, from which curve the interfacestate density and the fixed charge density were calculated. Both theinterface state density and the fixed charge density were smaller thanthose in the related art because of the small quantity of oxygen andcarbon impurities on the surface of Si film formed by the second stepafter the substrate cleaning in the first step, as shown in FIG. 15. Thephenomenon is the effect of the continuous treatment in a vacuum afterthe dry-cleaning.

The film-forming apparatus 1 illustrated in FIG. 1 has a controller toconduct entire process in a vacuum, provided for each process apparatusand each transfer apparatus. That is, a transfer controller 70 receivesthe input signal generated from the apparatus concerned, at input part,runs the transfer program which was programmed so that the processor mayoperate according to the flowchart, and thus outputs the action commandfor transferring the substrate to each process apparatus via the vacuumtransfer to the concerned apparatus. Process controllers A through D (71through 74) receive the input signal from the process apparatus, run theprogram which was programmed so that the treatment is operated accordingto the flowchart, and thus output the action command to the apparatusconcerned. The configuration of the controller 70 or controllers 71 to74 is the one given in FIG. 2, composed of an input part 82, a memorypart 83 having a program and data therein, a processor 84, and an outputpart 85. The configuration is basically a computer configuration, whichcontrols the concerned apparatus.

FIG. 9 illustrates the control of the transfer controller 70 and theprocess controllers A to D (71 to 74). In Step 610, a Si substrate withnative oxide film formed thereon is prepared. The transfer controller 70conducts control so as to transfer the substrate using the load-lockapparatus 50, (Step 611). Further the transfer controller 70 generatesthe command to the surface treatment apparatus 100 to establish thevacuum of 1E-4 Pa or lower vacuum level, then moves the substrate 5 intothe surface treatment apparatus 100 via the transfer chamber 60 to placethe substrate on the substrate holder. The process controller A 71controls the procedure of above-described first step of applying surfacetreatment to the substrate 5, (Step 613).

The transfer controller 70 controls the CVD film-forming apparatus 20 toevacuate to establish the vacuum of 1E-4 Pa or lower vacuum level, thenmoves the substrate 5 from the surface treatment apparatus 100 to theCVD film-forming apparatus 20 to place the substrate 5 therein via thetransfer chamber 60.

The process controller B72 controls the above-described second step oftreating single crystal growth in the CVD film-forming apparatus 20,(Step 615). Immediately after that, the process controller B72 moves thesubstrate into the dielectric-electrode sputtering apparatus 40 via thetransfer chamber 60 to conduct the third step of dielectric-electrodesputtering film-forming, (Step 616).

The process controller C73 controls the third step of film-formingtreatment in the dielectric-electrode sputtering apparatus 40, (Step617). The transfer controller 70 establishes the vacuum of 1E-4 Pa orlower vacuum level in the oxidation-nitrification apparatus 30, andmoves the substrate 5 from the dielectric-electrode sputtering apparatus40 into the oxidation-nitrification apparatus 30 via the transferchamber 60, (Step 618). The process controller D74 conducts control toexecute the fourth step in the oxidation-nitrification apparatus 30,(Step 619). Immediately after that, the process controller D74 moves thesubstrate 5 into the dielectric-electrode sputtering apparatus 40 viathe transfer chamber 60 to conduct the fifth step of metal electrodesputtering film-forming, (Step 620). The process controller C73 conductscontrol to execute film-forming treatment of example 3 in thedielectric-electrode sputtering apparatus 40, (Step 621). Then, thetransfer controller 70 opens the transfer chamber 60 to atmospheric airusing the load-lock apparatus 50, (Step 622).

By the above-described treatment of the present invention, the MOS fieldeffect transistor (FET) 90 illustrated in FIG. 19 was manufactured. AnHfO film was adopted as a dielectric gate insulation film 95 below agate electrode 94 between a source region 92 and a drain region 93 of aSi substrate 91. Other than HfO, preferable gate insulation film 95includes a film of Hf, La, Ta, Al, W, Ti, Si, Ge, or an alloy thereof,and more specifically there are applicable HfN, HfON, HfLaO, HfLaN,HfLaON, HfAlLaO, HfAlLaN, HfAlLaON, LaAlO, LaAlN, LaAlON, LaO, LaN,LaON, HfSiO, and HfSiON. The relative permittivity thereof is in a rangefrom 3.9 to 100, and the fixed charge density is in a range from 0 to1×10¹¹ cm⁻². The film thickness of the gate insulation layer is set to arange from 0.5 to 5.0 nm.

The term “fixed charge” is also referred to as “fixed oxide filmcharge”, meaning the charge existing in SiO₂ film and being fixedtherein, not migrating in electric field or the like. The fixed oxidefilm charge appears caused by a structural defect in the oxide film, anddepends on the formed state of the oxide film or the heat treatmentthereof. Normally there exists a positive fixed charge in the vicinityof Si—SiO₂ interface originated from a dangling bond of Si in silicon.The fixed oxide film charge makes the C-V characteristic of MOSstructure shift in parallel along the gate voltage axis. The fixedcharge density is determined by the C-V method.

As the gate electrode 94 of MOS-FET in FIG. 19, there are applied: metalsuch as Ti, Al, TiN, TaN, and W; polysilicon (B(boron)-dope: p-Type orP(phosphorus)-dope: n-Type); and Ni-FUSI (fully silicide).

The semiconductor/insulation film joint, which was prepared by themethod of the present invention, that is, by the method of treating thesurface of a Si substrate having native oxide film formed thereon,growing the Si single crystal film without exposing thereof toatmospheric air, sputtering for forming a dielectric film such as Hfwithout exposing the substrate to atmospheric air, and oxidizing andnitrifying thereof, gives smaller fixed charge and lower interface statethan those of the joint prepared in the atmospheric transfer. Therefore,the joint gives a C-V curve with small hysteresis as shown in FIG. 16,with small leak current, thereby providing good device characteristics.The term “interface state” signifies the energy level of electron beingappeared on interface of joint of different kinds of semiconductors andon interface of joint between a semiconductor and a metal or aninsulation material. Since the semiconductor face on the interfacebecomes a condition of breaking bond between atoms, there appears anon-bonding condition called the dangling bond, thus creating an energylevel to allow entrapping the charge. Also impurity or defect on theinterface creates an energy level allowing entrapping the charge, or aninterface state. Generally the interface state shows a long responsetime and is instable, thus often adversely affects the devicecharacteristics. Lower interface state means better interface. Theinterface state density is determined by the C-V method.

As illustrated in FIG. 1, the film-forming apparatus of the presentinvention uses the configuration having each one of: the surfacetreatment unit 100, the CVD film-forming unit 20, thedielectric-electrode sputtering unit 30, the oxidation-nitrificationunit 40, the load-lock chamber 50, and the transfer chamber 60. However,the quantity of each of those units is not necessarily one, and morethan one unit for there each can be applied depending on the throughput,the film structure, and the like. For example, to increase thethroughput, the load-lock chamber may be substituted by a plurality ofload-lock chambers allotting the functions of loading and unloading toeach one. Furthermore, for example, the sputtering unit 30 may besubstituted by two or more sputtering units allotting the functions offorming the dielectric film and forming the electrode to each one.

However, for effective use of the substrate treatment method whichallows conducting the dry substrate surface treatment while keeping flatsurface according to the present invention, it is preferable to have atleast one unit for each of the surface treatment unit 100, the CVDfilm-forming unit 20, the load-lock chamber 50, and the transfer chamber60. With this configuration, the presence of load-lock chamber makes thedry substrate surface treatment possible at high throughput in a stableevacuated atmosphere, and the film-forming by transferring the substrateto the CVD film-forming unit via the transfer chamber in a vacuumwithout exposing the substrate to atmospheric air allows keeping goodcondition of interface between the Si substrate surface and the CVDfilm-formed Si/SiGe layer.

In addition, to effectively use the substrate treatment method whichallows treating the dry substrate surface while keeping flat surfaceaccording to the present invention, it is preferable to have at leastone unit for each of the surface treatment unit 100, thedielectric-electrode sputtering unit 30, the load-lock chamber 50, andthe transfer chamber 60. With this configuration, the presence ofload-lock chamber makes the dry substrate surface treatment possible athigh throughput in a stable evacuated atmosphere, and the film-formingby transferring the substrate to the dielectric-electrode sputteringunit 30 via the transfer chamber in a vacuum without exposing thesubstrate to atmospheric air allows keeping good condition of interfacebetween the Si substrate surface and the dielectric film or conductivefilm as the base of the insulation film prepared by sputtering on the Sisubstrate surface.

Although the example does not give the detail of the CVD film-formingunit 20 in the drawing, any type of epitaxial film-forming unit isapplicable if only the unit is provided with a chamber, asubstrate-heating mechanism for heating both the substrate holder forholding the substrate and the substrate held thereto, a gas-feedmechanism for supplying a gas containing the raw material gas to conductthe CVD film-formation, and an exhaust means for discharging the chamberatmosphere.

Similarly the detail of the sputtering unit 30 is not given in thedrawing. The sputtering unit 30 may be, however, any type if only theunit has a chamber, a substrate holder for holding the substrate, amechanism for feeding the gas into the chamber, an exhaust means fordischarging the chamber atmosphere, a sputtering cathode for mountingthe target made of dielectric or conductive metal, and a high frequencypower supply mechanism or a direct current power supply mechanism.

The quantity of the sputtering cathode for mounting the target made ofdielectric or conductive metal, (not shown), in the sputtering unit 30is not necessarily one, and a plurality of sputtering cathodes may beapplied for forming a plurality of continuous or discontinuous films andfor mounting a plurality of targets thereon. From the point ofuniformity of the thickness distribution of the formed film, thesubstrate holder is preferably provided with a rotary mechanism torotate the mounted substrate. For allowing film-forming by reactivesputtering, the gas-feed mechanism of the sputtering unit 30 preferablyfeeds not only inert gas such as Ar but also a reactive gas such as N₂and O₂, or a mixture of reactive gas with Ar gas.

1.-22. (canceled)
 23. A method of treating a surface of semiconductorsubstrate placed in a treatment chamber, comprising the steps of:generating plasma by exciting a plasma-forming gas containing HF in aplasma-forming chamber; selectively feeding a radical in the plasma fromthe plasma-forming chamber to the treatment chamber; feeding a treatmentgas containing unexcited HF into the treatment chamber; and treating thesurface of the semiconductor substrate by an atmosphere of a mixture ofthe radical and the treatment gas, fed into the treatment chamber.
 24. Amethod of claim 23, wherein the treatment of gas contains at least HF bya fraction from 0.2 to 1.0 to the total amount of the treatment gas, andpreferably the treatment gas is composed of substantially HF.
 25. Amethod of claim 23, wherein the plasma-forming gas is composed ofsubstantially HF.
 26. A method of claim 23, wherein the selectivefeeding of the radical to the treatment chamber is conducted by feedingthe radical from the plasma chamber to the treatment chamber, allowingthe radical to pass through a radical-passing hole formed in aplasma-confinement electrode plate partitioning the plasma chamber fromthe treatment chamber, while rejecting ions in the plasma.
 27. A methodof claim 23, wherein the semiconductor substrate is a Si substrate, andthe cleaning treatment of the Si substrate is conducted after removingnative oxide film on the Si substrate by etching.
 28. A method offorming a gate insulation film of MOS structure, comprising the stepsof: cleaning the surface of a Si substrate by the method of claim 27;transferring the surface-cleaned Si substrate to an expitaxial chamberwithout exposing the Si substrate to atmospheric air, and forming anexpitaxial layer on the surface-cleaned Si substrate; transferring theSi substrate having the expitaxial layer formed thereon to a sputteringchamber without exposing the Si substrate to atmospheric air, andforming a dielectric film on the epitaxial layer by sputtering; andtransferring the Si substrate having the dielectric film formed thereonto an oxidation-nitrification chamber without exposing the Si substrateto atmospheric air, and oxidizing, nitrifying, or oxnitrifying thedielectric film to form the gate insulation film.
 29. A method of claim28, wherein the dielectric film is made of the one selected from thegroup consisting of Hf, La, Ta, Al, W, Ti, Si and Ge, or an alloythereof.
 30. An apparatus of treating a semiconductor substrate,including a treatment chamber for treating the surface of thesemiconductor substrate, comprising: a plasma-forming chamber generatingplasma by exciting a plasma-forming gas containing HF; means forselectively feeding a radical in the plasma from the plasma-formingchamber to the treatment chamber; and means for feeding a treatment gascontaining unexcited HF into the treatment chamber, and thus treatingthe surface of the semiconductor substrate by an atmosphere of a mixtureof the radical and the treatment gas, fed into the treatment chamber.31. An apparatus of treating a semiconductor substrate of claim 30,wherein the means for selectively feeding the radical to the treatmentchamber is a plasma-confinement electrode plate which partitions theplasma chamber from the treatment chamber, and the plasma-confinementelectrode plate has a radical-passing hole formed which connects theplasma chamber with the treatment chamber, thus feeding the radicalthrough the radical-passing hole from the plasma chamber to thetreatment chamber, while rejecting ions in the plasma.